I am really of the opinion that dirty laundry doesn't need to be aired in public; I also agree with Sponge that detailed negative posts about why a player is gone make people not involved uncomfortable. It really should just be as simple as:
'X has been banned from the game for a violation of our harassment policies. Please contact staff if you have any questions/need any resolution to stories.'
If someone's done something to deserve being banned, putting it up like that isn't going to do any harm.
Also, @JaySherman: Kill both player A and B with fire. Get rid of them: they are BOTH major problem sorts. They are not going to be any good for your game. Even a little bit. If it's a "friendship" that's being held hostage in any fashion, it's not actually a friendship and you're being used/manipulated.